Many natural and synthetic materials are known to be useful as lubricants, their utility in particular applications depending on factors such as their stability and viscosity under the conditions of use, their pour points, and their compatibility with any materials with which they will be used.
In refrigeration applications (e.g., home-use or industrial-use refrigerators, freezers, or air conditioners for buildings, automobiles, airplanes, and other vehicles), the need to replace chlorofluorocarbon refrigerants with a refrigerant having lesser ozone-depleting potential has made it important to find lubricants which would be suitable for use with 1,1,1,2-tetrafluoroethane (R-134a), a refrigerant that has been reported to have an ozone depletion potential of zero. Mineral oils, usually the refrigeration lubricants of choice in the past, cannot be utilized in this application because of incompatibility with R-134a.
As shown, e.g., in Jolley, "New and Unique Lubricants for Use in Compressors Utilizing R-134a Refrigerant," pp. 145-152 (a paper presented at the ASHRE/Refrigeration/Compressor Engineering Conference at Purdue University, July 1990), oils of various types, including polyalkylene glycols, esters, and amides, have been found to have sufficient compatibility with R-134a to justify further investigation. However, there is still a need for lubricants to be used in this application, as well as in other lubricant applications.
The Michael reaction is a known process wherein a Michael acceptor (such as an .alpha.,.beta.-ethylenically-unsaturated ester) is reacted with a Michael donor (such as a dialkyl malonate) to elongate a carbon chain. As indicated in Skarzewski, "The Michael Reaction of Methanetricarboxylic Esters. A Simple Method for Two-Carbon Chain Elongation." Synthesis, December 1990, pp. 1125-1127, it has usually been considered undesirable to add a donor molecule to more than one acceptor molecule in such a reaction. However, U.S. Pat. No. 2,396,626 (Wiest et al.) teaches that products useful as plasticizers or solvents can be obtained by reacting two molecules of an alkyl acrylate with a molecule of a donor, such as an ester of malonic acid, phenylacetic acid, cyanoacetic acid, or acetoacetic acid.
Copending application Ser. No. 07/947,628 (Sabahi) discloses ester oils corresponding to the formula ROOC-CH.sub.2 CH.sub.2 -(ROOC-CHCH.sub.2).sub.m -C(COOR).sub.2 -(CH.sub.2 CHCOOR).sub.n -CH.sub.2 CH.sub.2 -COOR in which the R's represent one or more alkyl groups of 1-30 carbons and the sum of m and n in the molecules is an average of 1-10. These ester oils can be prepared by a Michael reaction so as to have viscosities of 1-600 mm.sup.2.s.sup.-1 and have been discovered to be useful as refrigeration lubricants. Some of them, however, have insufficient compatibility with R-134a to be employed therewith.